Just recently I walked in on my 13-year-old niece, and she appeared to be masturbating. She has not been sexually active in any way at all. She hasn't even hit puberty yet. I talked to her about this, and she said she didn't know why but it helps her go to sleep and she does it almost every night before bed. I haven't gotten in contact with her parents yet, either, and don't know if this is normal or not.